This invention relates to tablet formulations for oral administration, particularly to formulations, which comprise a xcex2-lactam antibiotic, optionally together with a xcex2-lactamase inhibitor.
Many known tablet formulations which include a xcex2-lactam antibiotic are required to be taken orally three times a day. There is a need for oral formulations which need only be taken twice or less often per day. Methods of forming delayed or sustained release tablet formulations are known, for example coating the tablet with a release-retarding coating, or coating individual granules with such a coating, and compressing these coated granules into a tablet. xe2x80x9cRelease-retardingxe2x80x9d as used herein, unless otherwise defined, refers both to release which is retarded so as to be sustained, i.e. active material is released gradually from the tablet, and to release which is retarded so as to be delayed, i.e. release begins or the rate of release increases after an initial delay.
Particular problems occur in the preparation of delayed or sustained release forms of the known antibacterial combination of the xcex2-lactam antibiotic amoxycillin, in the form of its trihydrate, and the xcex2-lactamase inhibitor clavulanic acid, in the form of an alkali metal salt, such as potassium clavulanate. This is because amoxycillin trihydrate is relatively insoluble in aqueous media, whereas potassium clavulanate is extremely soluble, hygroscopic and moisture-sensitive, and it is difficult to achieve sustained or delayed release of two such components at a compatible rate from a single formulation containing both.
According to this invention, a tablet formulation comprises a core which includes a first pharmaceutically active material, the core being coated with a release retarding coating, the coated core being itself surrounded by a casing layer which includes a second pharmaceutically active material.
The tablet formulation of the invention is suitable for oral administration, and provides a sustained and/or delayed release as a result of initial quick release of the second active material from the casing layer, and a sustained or delayed release of first active material from the coated core. Also the casing layer may serve to protect the core from the ingress of air and atmospheric moisture. Also coating of a single relatively large core in the tablet of the invention with a release-retarding coating requires less coating material than is required to coat a large number of smaller granules, and can therefore lead to a relatively low tablet weight.
The first and second pharmaceutically active materials in the tablet formulation may each individually, and/or together, comprise a xcex2-lactam antibiotic optionally together with a xcex2-lactamase inhibitor. Suitably the xcex2-lactam antibiotic may be amoxycillin, e.g. in the form of its trihydrate, optionally together in combination with the xcex2-lactamase inhibitor clavulanate, (the term xe2x80x9cclavulanatexe2x80x9d used herein, unless otherwise identified, refers both to clavulanic acid and its salts) e.g. in particular potassium clavulanate. The first and second active materials may both comprise the same active material, for example both comprising a xcex2-lactam antibiotic optionally in combination with a xcex2-lactamase inhibitor. When both the first and second active materials comprise amoxycillin and clavulanate, the relative ratios of amoxycillin:clavulanate may be different in the core and the casing layer, making up the overall ratio in the tablet.
The amoxycillin:clavulanate ratios in the core and casing layer and the overall ratio may each vary between broad limits, e.g. between 30:1 to 1:1, typically 12:1 to 2:1. A preferred ratio is around 8:1 to 4:1xc2x125%.
The quantity of active material(s) in the tablet may vary up to the maximum allowed daily dose, and may typically be around a nominal single unit dose. For example in the case of amoxycillin and clavulanate, a single tablet may contain around 125, 250, 500, 750 or 875 mg of amoxycillin, and 62.5, 125 or 250 mg of clavulanate, both sets of weights being expressed in terms of the respective free acids. Typically the overall tablet may contain nominally 500 mg amoxycillin and 125 mg clavulanate, or 875 mg amoxycillin and 125 mg of clavulanate. Alternatively these weights may be divided between two or more tablets.
Typically for example the core may contain 25-75% of the total weight of the first and second components, and the casing layer may contain 75-25% thereof.
In the case of amoxycillin and clavulanate, in one embodiment both the core and the casing layer may contain clavulanate and amoxycillin. For example the core may contain 25-75% of the clavulanate and 25-75% of the amoxycillin, the balance being contained in the casing layer. For example the core may contain 100-400 mg of amoxycillin and 30-95 mg of clavulanate, expressed as the respective free acids. In an alternative embodiment, all of the clavulanate may be contained in the casing layer, e.g. in a rapid release form, with none of the clavulanate contained in the core. Such an embodiment may assist in maximising the clavulanate plasma level peak. In another alternative embodiment, all of the clavulanate may be contained in the core, with none of the clavulanate contained in the casing layer.
The core may be any convenient shape and need not necessarily be directly related to the shape of the overall tablet, typically the core may be spherical, ellipsoidal, or oblate spheroidal, within any suitable or convenient, e.g. a conventional, tablet shape.
The core and the casing layer may both comprise a compact of compressed ingredients including the respective active materials such as amoxycillin trihydrate optionally combined with potassium clavulanate. The active material(s) in the core may be present in a micronised or solubilised form. In addition to active materials the core and casing layer may contain additives conventional to the art of compressed tablets. Appropriate additives in such a tablet may comprise diluents such as calcium carbonate, magnesium carbonate, dicalcium phosphate or mixtures thereof, binders such as microcrystalline cellulose hydroxypropylmethylcellulose, hydroxypropyl- cellulose, polyvinylpyrrolidone, pre-gelatinised starch or gum acacia or mixtures thereof, disintegrants such as microcrystalline cellulose (fulfilling both binder and disintegrant functions) cross-linked polyvinylpyrrolidone, sodium starch glycollate, croscarmellose sodium or mixtures thereof, lubricants, such as magnesium stearate or stearic acid, glidants or flow aids, such as colloidal silica, talc or starch, and stabilisers such as desiccating amorphous silica, colouring agents, flavours etc. The core and casing layer may contain the same or different additives, in the same or different proportions.
The core may be made from a compacted mixture of its components, suitably in the form of granules, which may be made by a conventional granulating process as known in the art. Preferably the granules are made by a procedure of dry granulation of the granule components, for example milling, blending, slugging then milling, or by milling, blending or roller compaction then milling. The granules may include conventional additives introduced as a result of the granulation process, e.g. lubricants such as magnesium stearate, in conventional quantities, e.g. ca. 0.5-1 wt % of magnesium stearate. Suitably the granules are of 10-80 mesh size, suitably 10-40 mesh size, for example 16-30 mesh size.
The release-retarding coating may be a polymeric material, for example an enteric polymer (the term xe2x80x9centeric polymerxe2x80x9d is a term of the art referring to a polymer which is preferentially soluble in the less acid environment of the intestine relative to the more acid environment of the stomach).
An enteric coating may be an essentially conventional coating material, for example enteric polymers such as cellulose acetate phthalate, cellulose acetate succinate, methylcellulose phthalate, ethylhydroxycellulose phthalate, polyvinylacetatephthalate, polyvinylbutyrate acetate, vinyl acetate-maleic anhydride copolymer, styrene-maleic mono-ester copolymer, methyl acrylate-methacrylic acid copolymer, methacrylate-methacrylic acid-octyl acrylate copolymer, etc. These may be used either alone or in combination, or together with other polymers than those mentioned above. The enteric coating may also include insoluble substances which are neither decomposed nor solubilized in living bodies, such as alkyl cellulose derivatives such as ethyl cellulose, crosslinked polymers such as styrene-divinylbenzene copolymer, polysaccharides having hydroxyl groups such as dextran, cellulose derivatives which are treated with bifunctional crosslinking agents such as epichlorohydrin, dichlorohydrin, 1, 2-, 3, 4-diepoxybutane, etc. The enteric coating may also include starch and/or dextrin.
Preferred coating materials are the pharmaceutically acceptable methacrylic acid copolymer which are copolymers, anionic in character, based on methacrylic acid and methyl methacrylate, for example having a ratio of free carboxyl groups: methyl-esterified carboxyl groups of 1: greater than 3, e.g. around 1:1 or 1:2, and with a mean molecular weight of 135000.
Such polymers are sold under the trade name Eudragit(trademark), such as the Eudragit L series e.g. Eudragit L 12.5(trademark), Eudragit L 12.5P(trademark), Eudragit L100(trademark), Eudragit L 100-55(trademark), Eudragit L-30(trademark), Eudragit L-30 D-55(trademark), the Eudragit S(trademark) series e.g. Eudragit S 12.5, Eudragit S 12.5P(trademark), Eudragit S100(trademark), the Eudragit NE(trademark) series e.g. Eudragit NE 30D(trademark), the Eudragit RL(trademark) series, e.g. Eudragit RL 12.5(trademark), Eudragit RL 100(trademark), Eudragit RL PO(trademark), Eudragit RL 30D (trademark), and the Eudragit RS(trademark) series e.g. Eudragit RS 12.5(trademark), Eudragit RS 100(trademark), Eudragit RS PO(trademark), and Eudragit RS 30D(trademark).
Some of these polymers are known and sold as enteric polymers, for example having a solubility in aqueous media at pH 5.5 and above, such as the commercially available xe2x80x9cEudragitxe2x80x9d (Trade Mark) enteric polymers, such as xe2x80x9cEudragit L 30xe2x80x9d (Trade Mark) i.e. a cationic polymer synthesised from dimethylaminoethyl methacrylate, xe2x80x9cEudragit Sxe2x80x9d (Trade Mark) and xe2x80x9cEudragit NExe2x80x9d (Trade Mark).
Such polymers may be used either alone or with a plasticiser. Such coatings are normally applied using a liquid medium, and the nature of the plasticiser depends upon whether the medium is aqueous or non-aqueous. Aqueous plasticisers include propylene glycol or xe2x80x9cCitroflexxe2x80x9d or Citroflex A2xe2x80x9d (Trade Marks) (mainly triethyl citrate or acetyl triethyl citrate). Non-aqueous plasticisers include these, and also diethyl and dibutyl phthalate and dibutyl sebacate.
The quantity of plasticiser included will be apparent to those skilled in the art. The enteric coating may also include an anti-tack agent such as talc, silica or glyceryl monostearate. The quantity of plasticiser and anti-tack agent may be generally conventional to the art. Typically the coating may include around 10-25 wt. % plasticiser and up to around 50 wt % of anti tack agent, e.g. 5-20 wt. % of anti-tack agent.
An enteric coating may be applied to the core by dissolving or suspending the enteric coating materials in a suitable medium, such as water, methanol, ethanol, isopropanol, acetone, methyl ethyl ketone, methylene chloride, ethylene chloride, ethyl acetate, etc. or mixtures thereof, and the resultant solution or suspension may be sprayed on the core to coat them, followed by drying sufficiently with an air flow and screening.
In the case of the preferred enteric coating material referred to above, the enteric coating material may be dissolved or suspended in a solvent for example water and coated onto the core using a fluidised bed system. If water is used, preferably an anti-foaming agent such as activated polymethylsiloxane is also included.
It may be desirable, particularly in the case of cores which contain highly soluble or moisture sensitive active materials such as potassium clavulanate, to first apply one or more sub-coats to the core, before application of the release retarding coating layer, the sub-coat consequently lying beneath the release retarding coating. Suitable sub-coat materials include hydroxypropylmethyl cellulose, for example of the known types E5 and E15 (Trade Marks) in mixture. It may also be desirable to apply one or more over-coats after application of the release retarding coating layer, the over-coat consequently lying over the release retarding coating. Suitable over-coat materials include copolymers of methacrylic acid and methyl methacrylate, and hydroxypropylmethyl cellulose. The over-coat may be of the same material as the sub-coat. Typically such coatings may be applied by known techniques of aqueous film coating.
The casing layer may be applied to the coated core by a generally conventional process in which the coated core is encased in a mass of the powdered or granulated casing material components. The granules of such a casing material may be made by a conventional granulating process as known in the art, and as discussed above with reference to the manufacture of the core granules.
The casing layer itself may be coated with a final outer coating, for example of hydroxypropyl methyl cellulose, which may be applied by known film coating techniques in a similar manner to the way in which the sub-and over-coats may be applied to the core.
The tablet of the invention offers the advantages effect that the active material in the casing layer is released initially in the stomach, and the coated core releases its active material content more slowly. In this way as in vivo decay of the initially released material occurs, active material is subsequently released from the core to provide an extended blood level profile. If the release-retarding coating on the core is an enteric coating the release of active material from the core may occur in the intestine.
The invention therefore also provides a method of preparing a pharmaceutical formulation as described herein, comprising the steps of forming a core which includes a first pharmaceutically active material, the core being coated with a release-retarding coating, then coating the core with a casing layer which includes a second pharmaceutically active material.
Clavulanic acid and its derivatives, e.g. salts such as potassium clavulanate are extremely moisture sensitive, and all operations carried out to prepare granules and formulations of this invention which contain clavulanate should be carried out under conditions of low relative humidity, e.g. less than 30% RH, ideally as low as practical.
The present invention also provides a pharmaceutical formulation as described herein for use as an active therapeutic substance.
The present invention also provides a pharmaceutical formulation as described herein for use in the treatment of bacterial infections.
The present invention also provides the use of a formulation as described herein in the manufacture of a medicament for use in the treatment of bacterial infections.
The present invention also provides a method of treatment of bacterial infections in humans or animals which comprises the administration of an effective amount of a pharmaceutical formulation as described herein.